High sensitivity and broad range iontronic pressure sensor based on porous structure

Abstract

As technology advances, there is a growing demand for pressure sensors, particularly in the context of wearable devices. Traditional pressure sensors have rigid properties which is unsuitable for flexible devices. However, flexible pressure sensors are leading to the prominence of pressure sensors. Based on their mechanisms, flexible pressure sensors can be categorized into four types: piezoresistive, piezoelectric, triboelectric, and capacitive pressure sensors. Among these, capacitive sensors have gained attention for their ability to detect both static and dynamic forces, coupled with their simple structure and cost-effectiveness in device design and analysis.

Capacitive sensors typically consist of a dielectric layer and two electrodes, responding to applied pressure by inducing changes in capacitance. However, their sensitivity is limited due to the close proximity of the electrodes, making them less than ideal for wearable devices. In response to this challenge, researchers have focused on enhancing the sensitivity of capacitive sensors through various strategies.

Recent efforts to increase the sensitivity of flexible capacitive pressure sensors can be classified into three main strategies. The first involves incorporating air gaps within the dielectric layer or at the electrode-dielectric interface. The second strategy entails doping or coating polymers with high dielectric constants or conductive fillers. The third strategy involves introducing ionic conductors into the dielectric layer.

In this study, these three strategies are used to develop a capacitive sensor for increased sensitivity. Firstly, we used glucose as a template to add air gaps into dielectric layer based on polydimethylsiloxane (PDMS). Then, by mixing the carbon nanotubes (CNTs) with glucose to fabricate a porous elastomer coating with CNTs. Finally, introducing an ionic liquid (IL) with the proposed porous elastomer, a highly sensitive capacitive pressure sensor is achieved. The pressure sensor exhibits high sensitivity (~0.815kPa-1) in the high-pressure range (80−120 kPa). Furthermore, it delivers excellent performance with a fast response time (∼76 ms), in conjunction with high repeatability, reproducibility, and reliability (5 and 100 kPa/1000 cycles). Compared to traditional pressure sensors, the developed flexible pressure sensor has a broad detection range (0-120kPa). On the other hand, diverse applications of the developed sensor have been showed. The proposed pressure sensor is able to be applied in wearable devices to monitor the finger motion. Besides, we demonstrate the flexible sensor array integrated with fabricated sensors to detect the static force. At the same time, the proposed pressure sensors are conducted to make a plantar system to monitor the human motion.